CY7C64013
CY7C64113
Document #: 38-08001 Rev. **
Page 12 of 48
5.0
Programming Model
5.1
14-Bit Program Counter (PC)
The 14-bit program counter (PC) allows access to up to 8 KB of PROM available with the CY7C64x13 architecture. The top 32
bytes of the ROM in the 8 Kb part are reserved for testing purposes. The program counter is cleared during reset, such that the
first instruction executed after a reset is at address 0x0000h. Typically, this is a jump instruction to a reset handler that initializes
the application (see Interrupt Vectors on page 27).
The lower eight bits of the program counter are incremented as instructions are loaded and executed. The upper six bits of the
program counter are incremented by executing an XPAGE instruction. As a result, the last instruction executed within a 256-byte
“page” of sequential code should be an XPAGE instruction. The assembler directive “XPAGEON” causes the assembler to insert
XPAGE instructions automatically. Because instructions can be either one or two bytes long, the assembler may occasionally
need to insert a NOP followed by an XPAGE to execute correctly.
The address of the next instruction to be executed, the carry flag, and the zero flag are saved as two bytes on the program stack
during an interrupt acknowledge or a CALL instruction. The program counter, carry flag, and zero flag are restored from the
program stack during a RETI instruction. Only the program counter is restored during a RET instruction.
The program counter cannot be accessed directly by the firmware. The program stack can be examined by reading SRAM from
location 0x00 and up.
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